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From: Devils Advocaat on 20 Jul 2010 10:54
When a ball is attached to a pivot by a length of string and allowed
to move around in a circle, it presents the same face to the centre of
that circle all the time, I believe that the ball is actually rotating
about an axis perpendicular to the circular path it is moving along,
and that this axis is at the point of the circumference where the
string is attached.

However, an associate of mine says that if the ball was rotating that
the string would wind around the ball, so the ball cannot be rotating.
Can you advise me as to which of us is correct and why?
From: Cwatters on 21 Jul 2010 05:55

"Devils Advocaat" <mankygoat(a)yahoo.co.uk> wrote in message
news:129ab47a-456a-49b6-8b30-840806e901b9(a)r27g2000yqb.googlegroups.com...
> When a ball is attached to a pivot by a length of string and allowed
> to move around in a circle, it presents the same face to the centre of
> that circle all the time, I believe that the ball is actually rotating
> about an axis perpendicular to the circular path it is moving along,
> and that this axis is at the point of the circumference where the
> string is attached.
>
> However, an associate of mine says that if the ball was rotating that
> the string would wind around the ball, so the ball cannot be rotating.
> Can you advise me as to which of us is correct and why?

You are.

The string doesn't wind around the ball because the string is also rotating.

If the ball wasn't rotating the string would indeed wind around the ball.









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